This means that the conntrack database doesn't have enough entries for your environment. Connection tracking by default handles up to a certain number of simultaneous connections. This number is dependent on your system's maximum memory size (at 64MB: 4096, 128MB: 8192, ...). You can easily increase the number of maximal tracked connections, but be aware that each tracked connection eats about 350 bytes of non-swappable kernel memory!
To increase this limit to e.g. 8192, type this from the CM CLI: echo "8192" > /proc/sys/net/ipv4/ip_conntrack_max
Last updated: Aug 08, 2017